Understanding the Molecular Mechanisms that Contribute to Parkinson's Disease: Defining the Role of Ca2+ in TG2: ?-synuclein Macromolecular Complex Assembly

ECU Author/Contributor (non-ECU co-authors, if there are any, appear on document)

James Washington (Creator)

Institution

East Carolina University (ECU )

Web Site: http://www.ecu.edu/lib/

Abstract: "Transglutaminase 2 (TG2) is an allosteric enzyme ubiquitously expressed in human tissue. This versatile enzyme has both Ca2+ -dependent , transamidase and GTPase activities. TG2's Ca2+ -dependent transamidase activity is linked to many different diseases; most notably neurodegenerative diseases like Parkinson's. Initial Ca2+-dependent , TG2 mediated post-translational modification of pathogenic proteins - including [alpha]-synuclein , tau , and [beta]-amyloid--increases their aggregations potential. As the disease progresses , neuronal damage causes a loss of Ca2+ homeostasis (i.e. increasing intracellular Ca2+ concentrations) and further activation of TG2; these increased activities further facilitate the formation of pathogenic protein oligomers. As such , the exacerbated symptoms of neurodegenerative disease can , in part , be attributed to this destructive cycle. The allosteric mechanism by which Ca2+ controls TG2's transamidase activity is not fully understood. The currently accepted model posits that Ca2+ binding to TG2 prior to the protein substrate (i.e. [alpha]-synuclein) induces conformational changes necessary for substrate binding and catalytic turnover. However , our preliminary data , using [alpha]-synuclein as a model substrate , challenges this theory; our model indicates that Ca2+ binding occurs after enzyme-substrate complex formation. That is , Ca2+ activates the TG2: [alpha]-synuclein complex. In light of this data , we aim to answer the question ""What role does Ca2+ have in activating of the TG2: substrate complex?"" We hypothesize that Ca2+ binding to the complex increases the stability of the enzyme: substrate complex , thereby increasing the rate of catalysis. Using Surface Plasmon Resonance (SPR) , we have shown that the interactions between TG2 and [alpha]-synuclein do not adhere to a simple 1:1 binding model; as such , possible binding models for macromolecular complex formation are presented. We have also identified potential Ca2+- binding regions on TG2 using multiple alignments. We expect our findings will be beneficial in developing an accurate model for TG2 activation , which can further be used to develop therapeutics that inhibit activity."

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Language: English

Date: 2018

Keywords

TG2

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